Q-system

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Available Q system reagents - Flies (including QF2) 

Available Q system reagents - DNA (including QF2) 

Figure 1 (click to enlarge)


Q-system

 

The “Q-system” consists of three components: the QF transcription factor, the QS suppressor, and a QUAS-effector (Figure 1). The QUAS element contains 5 QF binding sites, and allows for robust QF-dependent expression of the effector.

We recently modified the QF transcription factor so that it is no longer toxic when broadly expressed.  This new version is called QF2. Details can be found in Riabinina, 2015. 

 

Intersectional expression

 

Figure 2 (click to enlarge)

By using the Q-system with the GAL4 system, effector gene expression can be limited to subsets of tissues or expression patterns not previously possible. In this case, the interaction between the QF expression pattern and the GAL4 expression pattern can be thought of as logical operations (Figure 2). For example, limiting expression to where only QF AND GAL4 are expressing is an “AND” logic gate . Alternatively, one could use any of the thousands of GAL4 lines available to carve out expression of a QF line. This would be an example of QF NOT GAL4 where expression is limited to where QF is expressed, but NOT where GAL4 is expressed. Conversely, one could use a QF line to carve out expression of a GAL4 line (GAL4 NOT QF). The genetic strategies for such expression pattern manipulations are summarized in the Figure 2.

 

 

 

Mosaic Analysis

By using differential expression of the QS suppressor, the Q-system can also be used for Mosaic Analysis with a Repressible Cell Marker: Q-MARCM (Movie). This is analogous to the GAL4 based MARCM system (Lee and Luo, 1999), yet requires no GAL4 components. In this technique, loss of the QS suppressor is directed by a mitotic recombination event that segregates the QS suppressor into one progenitor cell but not the other (see Movie). Since the GAL4 and Q-systems work independently in vivo, the GAL4 system could be used to inhibit function in a population of cells, and the Q-system could be used to determine the effect of such GAL4 mediated perturbations on a single neuron or cell. For example. GAL4 could be used to drive UAS-RNAi library expression in a target tissue, and the Q-system could be used to visualize the targeting of a single neuron to the target tissue in the background of such RNAi expression. Therefore, the use of the GAL4 and Q-systems together make investigations into non-autonomous effects more feasible.

Figure 3 (click to enlarge)

Since the Q-system and GAL4 system function independently in vivo, Q-MARCM and GAL4 MARCM can be coupled to the same mitotic event. As such, an unlabeled progenitor cell would give rise by mitosis to one cell that is positively labeled by the Q system (as it lacks the QS repressor), and a sister cell that is positively labeled by the GAL4 system (as it lacks the GAL80 repressor) (Movie ). This is called “coupled MARCM” as the segregation of the QS and GAL80 suppressor are coupled to the same mitotic event (Figure 3). 

For any questions regarding the Q-system, contact Chris Potter cpotter@jhmi.edu